FRANKFURT, Germany (AP) — German automaker Daimler AG says prosecutors will be searching several of its offices in Germany as part of a preliminary investigation into suspected manipulation of diesel emission controls.

Daimler said Tuesday it was cooperating with the probe conducted by prosecutors in its home base of Stuttgart. The company had already disclosed the probe in its financial reports. It said the investigation focused on "known and unknown employees" of the company.

The company declined further comment.

Daimler said in its first-quarter earnings report that authorities in the U.S. and Europe had asked it for information about test results and the control systems used on its Mercedes-Benz cars. It said the U.S. Justice Department had asked the company to conduct an internal investigation.